1. Technical Field of the Invention
The present invention relates generally to a gas sensor which may be employed in an air-fuel ratio control system for automotive vehicles for measuring the concentration of gas such as O2, NOx, or CO, and more particularly to an improved compact structure of such a gas sensor and a production method thereof.
2. Background Art
It is known that control of burning of an internal combustion engines as a function of the concentration of oxygen contained in exhaust gasses and the air-fuel ratio of a mixture is effective in the energy saving and the emission control. As one of gas sensors suitable for measuring the concentration of oxygen in exhaust gasses, a gas sensor including a solid electrolyte body made of zirconia is known. This type of gas sensor is, however, required to be reduced in size and production costs and improved in durability and reliability. The approach to satisfaction of these requirements has still left room for improvement.
It is therefore a principal object of the present invention to provide a gas sensor designed to meet the above discussed requirements in a conventional structure of a gas sensor.
According to one aspect of the invention, there is provided a gas sensor which comprises: (a) a gas sensing element having an gas-exposed portion; (b) a hollow housing having a first and a second end, the housing holding the gas sensing element therein so as to arrange the gas-exposed portion outside the housing for exposure to a gas to be measured; (c) a protective cover installed on the first end of the housing to cover the gas-exposed portion of the gas sensing element; (d) leads connecting with the gas sensing element, extending from the second end of the housing for electrical communication with an external device; (e) a metallic cover installed on the second end of the housing, the metallic cover including a small-diameter portion, a large-diameter portion, and a shoulder portion connecting the smaller-diameter portion and the large-diameter portion; and (f) an insulator including a body and a flange projecting from the body, having disposed therein the leads connecting with the gas sensing element, the body having an outer diameter smaller than an inner diameter of the small-diameter portion of the metallic cover and being disposed within the small-diameter portion, the flange having a first and a second end surface opposed to each other and an outer diameter which is smaller than an inner diameter of the large-diameter portion of the metallic cover and which is greater than the inner diameter of the small-diameter portion, the insulator being disposed in the metallic cover with the first end surface of the flange urged by an elastic member to bring the second end surface into constant engagement with an inner wall of the shoulder portion of the metallic cover.
In the preferred mode of the invention, the metallic cover has a given length. The elastic member is so designed as to produce a first pressure acting on an inner wall of the large-diameter portion of the metallic cover in a radial direction of the large-diameter portion and a second pressure acting on the second end surface of the flange of the insulator in a lengthwise direction of the metallic cover perpendicular to the radial direction of the metallic cover.
The elastic member includes an annular plate and tabs. The annular plate has a diameter smaller than the inner diameter of the large-diameter portion of the metallic cover. The tabs projects from the annular plate so as to establish elastic engagement with the inner wall of the large-diameter portion of the metallic cover.
The elastic member also include guide protrusions each of which is disposed between adjacent two of the tabs and which projects from the annular plate to a circular line smaller than the inner diameter of the large-diameter portion of the metallic cover.
The elastic member may be made of a plate member having opposed surfaces which are symmetrical with each other.
The tabs of the elastic member may be so designed that when the insulator is inserted into the metallic cover, some of the tabs are bent elastically in a first direction away from one of the opposed surfaces of the annular plate by elastic pressure produced by the insertion of the insulator, while the other tabs are bent elastically in a second direction opposite the first direction.
The tabs may extend from the annular plate at an angle of approximately 45xc2x0 or more to one of the opposed surfaces of the annular plate.
The elastic member may also include a protrusion formed on one of the opposed surfaces thereof.
At least one of the opposed surfaces of the elastic member is painted so that the opposed surfaces have different colors.
The tabs of the elastic member may alternatively be so designed that when the insulator is inserted into the metallic cover, the tabs are bent elastically in the same direction away from one of the opposed surfaces of the annular plate by the elastic pressure produced by the insertion of the insulator.
An elastic insulating member is disposed on an end of the metallic cover remote from the housing to retain the leads therein. If an outer diameter of the elastic insulating member is defined as E, and an outer diameter of the insulator is defined as F, then Exe2x89xa7F.
According to the second aspect of the invention, there is provided a gas sensor which comprises: (a) a gas sensing element having an gas-exposed portion; (b) a hollow housing having a first and a second end, the housing holding the gas sensing element therein so as to arrange the gas-exposed portion outside the housing for exposure to a gas to be measured; (c) a protective cover installed on the first end of the housing to cover the gas-exposed portion of the gas sensing element; (d) leads connecting with the gas sensing element, extending from the second end of the housing for electrical communication with an external device; (e) an insulator retaining therein the leads connecting with the gas sensing element; and (f) a metallic cover joined directly to the housing to hold the insulator therein.
In the preferred mode of the invention, the housing has an outer wall extending between the first and second ends. The metallic cover is welded to the whole of a circumference of the outer wall of the housing.
A welded portion is formed with welding of the metallic cover and the housing which includes a wider portion formed in the metallic cover and a narrower portion formed in the outer wall of the housing. If maximum widths of the wider and narrower portions are defined as A and B, respectively, the depth of the narrower portion is defined as D, and the thickness of the metallic cover 3 defined as T, conditions of Bxe2x89xa70.6 A and Dxe2x89xa7T are satisfied.
An elastic insulating member is disposed on an end of the metallic cover remote from the housing to retain the leads therein. If an outer diameter of the elastic insulating member is defined as E, and an outer diameter of the insulator is defined as F, then Exe2x89xa7F.
According to the third aspect of the invention, there is provided a gas sensor which comprises: (a) a gas sensing element having an gas-exposed portion; (b) a hollow housing having a first and a second end, the housing holding the gas sensing element therein so as to arrange the gas-exposed portion outside the housing for exposure to a gas to be measured; (c) a protective cover installed on the first end of the housing to cover the gas-exposed portion of the gas sensing element; (d) leads connecting with the gas sensing element, extending from the second end of the housing for electrical communication with an external device; (e) an insulator retaining therein the leads connecting with the gas sensing element; and (f) a metallic cover having a given length, the metallic cover being joined to the housing to hold the insulator therein in engagement of an end of the metallic cover to the housing.
An elastic insulating member is disposed on an end of the metallic cover remote from the housing to retain the leads therein. If an outer diameter of the elastic insulating member is defined as E, and an outer diameter of the insulator is defined as F, then Exe2x89xa7F.
According to the fourth aspect of the invention, there is provided a gas sensor which comprises: (a) a gas sensing element having an gas-exposed portion; (b) a hollow housing having a first and a second end, the housing holding the gas sensing element therein so as to arrange the gas-exposed portion outside the housing for exposure to a gas to be measured; (c) a protective cover installed on the first end of the housing to cover the gas-exposed portion of the gas sensing element; (d) leads connecting with the gas sensing element, extending from the second end of the housing for electrical communication with an external device; (e) an insulator retaining therein the leads connecting with the gas sensing element; and (f) a metallic cover joined to the housing to hold the insulator therein. The hollow housing has an inner chamber and an open end. The open end is crimped to elastically press a metal ring, a sealing member, and an insulating member disposed within the inner chamber to hold the gas sensing element in the inner chamber.
The housing has formed on the inner chamber a step. The gas sensing element has a protrusion which is urged elastically through the metal ring, the sealing member, and the insulating member by crimping the open end of the housing into constant engagement with the step of the housing.
The metal ring is made of a given length of a round bar which is looped.
The gas sensing element is made of a cup-shaped member having formed therein a chamber and has a platinum-made outer electrode formed on the gas-exposed portion and a platinum-made inner electrode formed on an inner wall thereof. A heater is disposed in the chamber of the gas sensing element.
A spring steel-made outer terminal is electrically connected to the outer electrode of the gas sensing element. A spring steel-made inner terminal is electrically connected to the inner electrode. The outer terminal has a conductive extension which is connected to the end portion of one of the leads within the insulator. The inner terminal has a conductive extension which is connected to the end portion of the other of the leads within the insulator and a heater-holding portion which holds the heater in the chamber of the gas sensing element.
The heater is formed with a plate heater which has a rectangular cross section and which is made of a lamination of a substrate formed with a ceramic sheet and a heat generating member.
The housing has an annular groove formed in the first end and an annular skirt extending from the first end around an outer circumference of the annular groove. The protective cover is made of an assembly of an outer cylindrical member and an inner cylindrical member. The outer and inner cylindrical members has flanges which are fitted in the annular groove of the housing. The annular shirt of the housing is crimped inward to elastically press the flanges of the outer and inner cylindrical members together within the annular groove to join the metallic cover to the housing.
An elastic insulating member is disposed on an end of the metallic cover remote from the housing to retain the leads therein. If an outer diameter of the elastic insulating member is defined as E, and an outer diameter of the insulator is defined as F, then Exe2x89xa7F.
According to the fifth aspect of the invention, there is provided a production method of a gas sensor including a gas sensing element having an gas-exposed portion, a hollow housing having a first and a second end portion, holding the gas sensing element therein so as to arrange the gas-exposed portion outside the housing for exposure to a gas to be measured, a protective cover installed on the first end portion of the housing to cover the gas-exposed portion of the gas sensing element, leads connecting with the gas sensing element, extending from the second end portion of the housing for electrical communication with an external device, an insulator retaining therein the leads connecting with the gas sensing element, and a metallic cover joined to the housing to hold the insulator therein. The production method comprises the steps of: (a) preparing an assembly of the housing and the metallic cover attached to an outer wall of the second end portion of the housing; (b) rotating the assembly around a central axis thereof; (c) keeping a rotational speed of the assembly at a given constant value; and (d) emitting a laser beam to a circumference of the metallic cover of the assembly to weld the metallic cover to the housing.
In the preferred mode of the invention, the assembly is rotated with the housing oriented upward and the metallic cover oriented downward.
A difference between an outer diameter of the outer wall of the second end portion of the housing to be welded to the metallic cover and an inner diameter of the metallic cover, that is, the inner diameter of the metallic cover minus the outer diameter of the housing falls within a range of xe2x88x920.15 mm to 0.1 mm.